In Exodus we read about the structure of the altar for burning incense:

You shall make an altar for burning incense; make it of acacia wood. It shall be a cubit long and a cubit wide—it shall be square—and two cubits high, its horns of one piece with it. Overlay it with pure gold: its top, its sides round about, and its horns; and make a gold molding for it round about. And make two gold rings for it under its molding; make them on its two side walls, on opposite sides. They shall serve as holders for poles with which to carry it. Make the poles of acacia wood, and overlay them with gold.—Exodus 30:1-5 (NJPS)

The altar and the poles to hold it are made of acacia overlaid with gold, but it sounds like the rings that serve has holders for the poles are pure gold. The trouble with that, I imagine, is that gold is soft and heavy, so it doesn't make the best structural material. A ring made out of something else overlaid with gold sounds more practical. Does the text support that reading?

3 Answers
3

The text just says "make" (in the Hebrew too) and this does not imply overlaying some other material, but the text provides an interesting hint.

Ex. 30:1-5 is the command, as quoted in the question. The actual construction is described in 37:25-27, where the same language is used:

25 And he made the altar of incense of acacia-wood [...] 27 And he made for it two golden rings under the crown thereof, upon the two ribs thereof, upon the two sides of it, for holders for staves wherewith to bear it.

Ok, so so far this only tells us that Bezalel "made" rings; it doesn't say how. Now look at the command to build the ark (Ex 25:12):

10 And they shall make an ark of acacia-wood: [...] 12 And thou shalt cast four rings of gold for it, and put them in the four feet thereof; and two rings shall be on the one side of it, and two rings on the other side of it.

This is what he does (37:1-3):

3 And he cast for it four rings of gold, in the four feet thereof: even two rings on the one side of it, and two rings on the other side of it.

For the altar it says "make"; for the ark it says "cast". Since the tabernacle is arguably the holiest construction project commanded to this generation, specified by God Himself, one could reason that precise language means something. So while we don't know what "make" means exactly with respect to the altar, it could be argued that it does not mean "cast from pure gold", because the text would have used a different word for that (like the ark). Whether "make" means "fabricate from pure gold in some other fashion", "fabricate from something else and gold-plate", or something else, the text does not tell us.

I wonder what the relative weights of the ark and the incense altar would have been...

Please note: This answer was written for a neutral, academic audience
and is not intended to be interpreted in the context of a religious
belief or doctrine.

If their gold casting techniques had not changed from the time they left Mt. Sinai, then the gold was not pure.

Ex 32:4 And he received [them] at their hand, and fashioned it with a
graving tool, after he had made it a molten calf: and they said, These
[be] thy gods, O Israel, which brought thee up out of the land of
Egypt.

Ex 32:20 And he took the calf which they had made, and burnt [it] in
the fire, and ground [it] to powder, and strawed [it] upon the water,
and made the children of Israel drink [of it].

Pure gold does not grind to a powder, but a gold-silica mix does. The silica makes the gold hard, and even brittle, while the gold makes the silica soluble which can be used to alloy pure gold and harden it.

It is plausible that they drank a water-gold-silca mix since they are all effectively inert ingredients.

Though we don't know the exact composition of the gold used in casting in the wilderness, the material described in Ex 32 was certainly not pure gold, and it is therefore likely that the cast gold ring in the OP were of a similar material. Since there is no record of the rings stretching or breaking, and the only case of the ark falling was off the back of a cart, the rings were sufficiently hard to not stretch and sufficiently tough to not have brittle fractures under the load.

Side Note: If I remember correctly, Gold alloys in the Americas included copper to stiffen it. The least bit of moisture, and galvanic action destroyed it.

This is a good point, though it's also worth considering that Aharon (no known goldsmithing skills) and Bezalel (identified as a craftsman) might not have done it the same way. Thanks for explaining how gold does (and doesn't) behave!
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Gone QuietJun 13 '12 at 2:56

Do you think that Isaiah was referencing Aaron? He starts with the birth pf Israel and then suggests a goldsmith was hired.
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Bob JonesJun 13 '12 at 3:34

3 Hearken unto me, O house of Jacob, and all the remnant of the house of Israel, which are borne by me from the belly, which are carried from the womb: 4 And even to your old age I am he; and even to hoar hairs will I carry you: I have made, and I will bear; even I will carry, and will deliver you. 5 ¶ To whom will ye liken me, and make me equal, and compare me, that we may be like? 6 They lavish gold out of the bag, and weigh silver in the balance, and hire a goldsmith; and he maketh it a god: they fall down, yea, they worship.
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Bob JonesJun 13 '12 at 3:34

1

As a leader, it may be said he made it even if he commissioned it to be made. Solomon built a temple...
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Bob JonesJun 13 '12 at 3:36

1

I was suggesting that perhaps Aaron 'hired' or commissioned smiths to do it. But took responsibility for it.
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Bob JonesJun 13 '12 at 18:53

If the rings are on the bottom, as v12 seems to indicate, then I would see no problem with them being solid gold, since they're more for "containment" of the poles than to support then entire weight via suspension.

Gold is not the most structurally-sound material in tension, but in compression it's certainly strong enough for the purpose at hand.

nice. so now the question becomes whether or not the weight is distributed well enough to ensure that the combined tensile strength of the gold rings is not exceeded. (Tensile strength 70-120 MPa)
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swasheckJun 12 '12 at 18:12

1

@swasheck - a gold abr at the bottom of the stack in Ft Knox isn't appreciably different in shape from one at the top - and each one is 30lbs, give or take
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warrenJun 12 '12 at 19:59